The abnormal regulation of insulin signalling in insulin-resistant subjects is associated with inadequate suppression of soluble protein tyrosine phosphatase (PTPase) activity in skeletal muscle (Sommercorn, CDNS, NIDDK). Multiple PTPases are likely to be involved in the signalling cascade. SH2-Domain PTPases are a class of PTPases selected as candidates for regulating tyrosine phosphorylation following insulin stimulation since it has been reported that such PTPases associate with several receptors and the post-receptor target, IRS1. SH2-Domain PTPase expression was detected in FAO cells, a rat insulin-sensitive hepatoma cell line, and in C2C12 cells, a mouse muscle cell line, using RT-PCR and degenerate primers (Sell, CDNS, NIDDK). These cell lines represent the two insulin-sensitive tissues reported to exhibit a drop in soluble PTPase activity following insulin stimulation: hepatic and skeletal muscle tissues. Sequence analysis of the amplified products revealed a high degree of identity with the hematopoietic SH2-D0omain PTPase, PTP1C. A related SH2-Domain PTPase, PTP1D, has since been reported to be expressed in liver and skeletal muscle. Experiments will be conducted in the future to characterize the regulation of SH2-Domain PTPases in insulin-responsive cells (FAO and C2C12) and skeletal muscle by insulin. RNA levels will be compared in insulin-resistant and sensitive subjects. Antibodies, specific for PTP1C and PTP1D and generously provided by the laboratory of Dr. Axel Ullrich (Max-Planck), will be used to compare protein levels. Basal levels as well as levels following insulin stimulation will be compared. The predicted amino acid sequence will also be compared in Pima subjects.